Hemoglobin S–Beta-Thalassemia Disease
(See also Overview of Hemolytic Anemia.)
Because of the increased frequency of both hemoglobin (Hb) S (the abnormal hemoglobin that is responsible for sickle cell disease) and beta-thalassemia genes in people of African, Mediterranean, or Southeast Asian ancestry, inheritance of both defects is relatively common. Beta-thalassemia results from decreased production of the beta-polypeptide chains of hemoglobin due to either mutations or deletions in the beta globin gene, leading to impaired production of hemoglobin A (see also Thalassemias).
Beta globin mutations may result in partial loss (beta + allele) or complete loss (beta 0 allele) of beta globin function. Thus, manifestations of S-beta-thalassemia depend on whether the patient has a beta + or beta 0 allele. Those with beta + produce varying amounts of beta globin (and thus have varying amounts of Hb A). Those with beta 0 produce no beta globin and thus have no Hb A.
Clinically, manifestations depend on the amount of Hb A. Thus, Hb-S-beta 0 thalassemia manifests similarly to sickle cell disease (Hb SS), whereas Hb S–beta+ thalassemia causes symptoms of moderate anemia and some signs of sickle cell disease, which are usually less frequent and less severe than those of pure sickle cell disease. Mild to moderate microcytic anemia is usually present along with some sickled red blood cells on stained blood smears.
Diagnosis requires quantitative hemoglobin studies. Hb S predominates on electrophoresis and is always greater than 50%.Hb A is decreased Hb-S-beta + or absent in Hb-S-beta 0. Hb F increase is variable.
Treatment, if necessary (eg, for symptomatic anemia, painful crises, end-organ disease), is the same as treatment of sickle cell disease.